Shell and tube-type heat exchangers customarily comprise a bundle of tubes mounted in spaced parallel relation at opposite ends in tube sheets. The tube bundle is surrounded by a shell through which a medium is flowed between an inlet and an outlet of the shell. Heads are provided on opposite ends of the shell to afford the flow of another medium through the interior of the tube bundles. In multiple pass heat exchangers, one head end of the heat exchanger may be provided with flow reversing means to cause the fluid to flow within selected tubes and make several passes before exiting the heat exchanger.
Heat exchangers of the above type have been known to fail in use and to require repair. Generally, this is accomplished by removing the head at opposite ends of the tube, and either removing, or replacing, the defective tube, or plugging the defective tube. Since such heat exchangers are often integral components of continuous plant processes, it is important that they be repaired quickly within a minimum of downtime.
Various types of plugs are known for sealing off defective tubes. For instance, U.S. Pat. Nos. 2,856,963; 4,393,564; 4,425,943; and 4,436,117 all relate to expandable plugging devices for use in shell and tube-type heat exchangers as described above. A typical plug assembly comprises a radially deformable sleeve adapted to be placed in a tube of a heat exchanger in alignment with its tube sheet and an elongated wedge slidably received within the sleeve for expanding the sleeve outwardly when pulled axially relative to the sleeve. A breakaway member is mounted at the narrow end of the wedge and is connected to a pull rod which cooperates with a compression tube engaging the sleeve to pull the wedge into the sleeve and expand it outwardly to provide a fluid type joint. After a predetermined amount of outward pressure has been applied, the breakaway ruptures to permit removal of the pull rod and compression tube from within the plugged tube.
While the aforementioned plug assemblies and associated placement apparatus function entirely satisfactory for their intended purposes, it has been found that the creation of an effective seal in a specific sized heat exchanger tube is difficult to accomplish because the stated size is often different then the actual size of the inner diameter. The inner diameters of heat exchanger tubes may vary due to variations in manufacturing tolerances and the formation of scale and corrosion. A plug assembly must be able to accommodate these conditions and still effect a strong seal. Hence, a plug assembly which can successfully apply an effective seal on a wide range of tube inner diameter tolerances and conditions is particularly desirable.